An inductor is a passive device which is used to store energy in a magnetic field and may be used in many integrated circuits, such as radio-frequency (RF) circuits. Inductors have measurable inductance (L), which is a measure of the magnetic field generated from the conductor. Inductance may vary according to the number of loops, loop sizes, wire diameter, etc. that make up the inductor. It is often desirable that the inductors have high inductance values. High inductance values, however, may be difficult to achieve on integrated circuits because of various intrinsic characteristics of the inductor itself such as resistance and capacitance, as well as some inductive effects such as eddie currents, which may have an adverse effect on the surrounding semiconductor substrate and/or surrounding circuits.
The resistive and capacitive components of the inductor may adversely affect the Q-factor (Quality) and FSR (Self-Resonant Frequency) of the inductor. The Q-factor is a measure of the inductors efficiency and is a ratio of the inductance to its resistance at a given frequency. Higher Q-factor values indicate a lower rate of energy loss. The FSR of an inductor is the natural frequency in which it oscillates freely.
Eddy currents are magnetic waveforms given off by the energized inductor. These currents are generally induced into the surrounding conductive materials when a conductor is exposed to a changing magnetic field. Eddy currents are circulating flows of electrons surrounding the body of the conductor. Eddie currents generate electromagnetic forces which cause heating and power loss when applied to the inherent resistive and capacitive components present in the substrate. This power loss may in turn adversely affects the Q and FSR components of an inductor.